1. Field of the Invention
The present invention relates to an ultrasound contrast agent that uses particles specifically targeting a liver site, and a method for preparing the ultrasound contrast agent.
2. Description of the Related Art
Ultrasound (US) imaging is the most frequently used imaging modality during diagnosis in clinical fields. It has no time-delay to obtain images, and is relatively cheap, non-invasive, safe, and easy for handling. To obtain more advanced information by ultrasound imaging, various ultrasound contrast agents have been developed, and applied to diagnosis. In general, most of them are microbubbles which are composed of gas cores such as N2 or perfluorocarbons and outer shells such as lipids or polymers. Ultrasound contrast agents can oscillate in response to acoustic pulse and provide bright signals in ultrasound images. Consequently, the localization and movement of these bright signals have been used for precise ultrasound imaging such as blood flow analysis.
In this century, the target-specific delivery of ultrasound contrast agents has garnered large amount of attention from many researchers. It is based on biological interactions and can provide molecular-level information as well as anatomical one. These targeted ultrasound contrast agents have been developed by conjugating antibodies, aptamers, or peptides on their shell. They can bind to special receptors on the surface of target cells and increase the accumulation of ultrasound contrast agent in target site.
Hyaluronic acid (HA) is one of the human body glycosaminoglycans and is non-toxic and biodegradable in body condition by enzymes like hyaluronidase. The chemical structure of hyaluronic acid is repeating disaccharides of N-acetyl-D-glucosamine and D-glucuronic acid bearing many carboxylic acids which can be used for further chemical modification. Especially, hyaluronic acid can bind to CD44 receptors which are overexpressed in liver. Consequently, hyaluronic acid can be used as attractive component of imaging agents to increase the target-specific delivery of ultrasound contrast agents for optical or MR imaging of liver.